Vantablack Pudding

Amorphous. The pudding can move through a space as narrow as 1 inch wide without squeezing.

Corrosive Form. A creature that touches the pudding or hits it with a melee attack while within 5 feet of it takes 12 (3d8) acid damage. Any weapon made of metal or wood that hits the pudding, nonmagical or magical, corrodes. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed. If a magic weapon is destroyed, it immediately recharges the pudding's Energetic Release action. 

Ammunition, magical or nonmagical, made of metal or wood that hits the pudding is destroyed after dealing damage.

The pudding can eat through 5-inch-thick wood or metal in 1 round.

Spider Climb. The pudding can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Magical Weapons. The puddings attacks are considered magical.

Multiattack. The pudding makes two pseudopod attacks. If a magic item has been destroyed by the pudding on or before its current turn, it can also use its Energetic Release. 

Pseudopod. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 12 (3d6 + 4) bludgeoning damage plus 24 (6d8) acid damage. In addition, armor worn by the target is partly dissolved and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10. This includes both magical and nonmagical armor. If a magic piece of equipment is destroyed, it immediately recharges the pudding's Energetic Release action. 

Energetic Release (Recharge 6). The pudding releases the energy from the magic items it has eaten at its foes. It cannot control what effect it does. Roll a d6 to select what effects the pudding performs. The effect must hit a creature that is hostile to the pudding. 

1: The target regenerates 2d4+2 hit points. 

2: The target must make a DC 16 CON save or take 15 (5d6) poison damage.

3: The target must succeed a DC 16 CHA Save or it becomes charmed by the pudding. While charmed in this way, their only desire is to jump into the slime, and must move all of their movement before they may repeat the save. 

4: 1d4 targets of the pudding's choice must make a DC 16 WIS save or take 9 (3d6) psychic damage.

5: The target must make a DC 16 INT save or it becomes stunned, and its INT stat drops by 1d4. The creature can repeat the save on the end of its turns, ending the effect on itself on a success, but the INT stat must be restored with Greater Restoration or similar magic, or a long rest. 

6: The target must make a DC 16 CON Save or its current hit point total is halved. If the creature is at 1 hit point when this affects it, it dies instantly.  

Split. When a pudding that is Medium or larger is subjected to lightning or slashing damage, it splits into two new puddings if it has at least 10 hit points. Each new pudding has hit points equal to half the original pudding's, rounded down. New puddings are one size smaller than the original pudding.